(1) Field of the Invention
The present invention relates to a method for interpolating missing pixels when image is expanded, and to an apparatus for a tone-image employing this method, such as a television, a video player, a video recorder, and a printer.
(2) Description of the Related Art
With rapid progress in the field of digital and highly integrated data, there has been an increasing need to improving a method for interpolating missing pixels that makes it possible to use existing data source as fully as possible.
Conventionally, the missing pixels are interpolated by a method using a linear function, by which approximate values of them (pixel data, such as a luminance expressed by its values) are computed by internally dividing those of neighboring pixels. For example, when an image is expanded four times in a specific ratio, the pixels symbolized by .largecircle. as shown in FIG. 1(a) are interpolated with the missing pixels symbolized by X, .gradient. and .increment. as shown in FIG. 1(b): as a matter of fact, the values thereof are the average of values of four neighboring pixels; that of two pixels neighboring to the left and right; and that of two pixels neighboring vertically.
However, the above conventional method has been plagued with three following problems:
1) Using the average of values makes differences in value between the pixels and missing pixels interpolated relatively small, therefore a boundary of luminance becomes unclear, making the image blurred and degrading resolution in an expanded image.
2) Although the differences in value, appearing as the diagonal line, looks substantially straight in an image, it is, in fact, a notched line as shown in FIG. 2(a) if seen in a pixel level. These notches are expanded accordingly as shown in FIG. 2(b), causing the diagonal line to appear a notched line in the expanded image.
3) Any noise contained in the pixels is subject to expansion as well, hence expanded inevitably.
Therefore, to devise an improved method for interpolation that overcomes these problems and an exemplary apparatus thereof has a great significance in meeting the need of today's image technology.